Process for drawing a continuous, unwashed, undrawn polycapolactam filament



3,111,364 PROCESS FOR DRAWING A CONTINUOUS, UNWASHED, UNDRAWN Nov. 19,1963 A. F. G. MEERDINK POLYCAPROLACTAM FILAMENT Flled Aprll 2a, 1960ANTON F. 6. MEERDINK BYWfM ATTORNEY United States Patent PRQCESS FGRDRAWING A CQNTINUOUS, UN-

WASEED, UNDRAWN PQLYCAERSLACTAM FEAMENT Anton Frederik George Meerdinh,Velp, Netherlands, as-

signor to American Erika Corporation, Erika, Nil, a corporation ofDelaware Filed Apr. 28, 1960, Ser. No. 25,257 Claims priority,appiication Netherlands May 13, 1959 5 Claims. (Ci. 1848) This inventionrelates generally to synthetic linear polycaprolactam yarns and threadsand more particularly to synthetic linear polycaprolactam for use inknitted articles and to a process for producing the same.

In the prior art, polycaprolactam threads and yarns which have been colddrawn and then twisted are used in knitted articles. The stitches inthese articles are long and narrow with the result that the article isnarrower than those produced from polyhexamethylene adipamide. More yarnis thus required to produce the same size article with the attendantincrease in cost.

In addition, the snag resistance of the articles knitted frompolycaprolactam yarn is very poor. Snag resistance is the ability or"the knitted article to resist the pulling out of the stitches. A stitchthat has been pulled out or snagged will project outwardly from thearticle in the form of a small loop.

It has been proposed that these difficulties of polycaprolactam yarns beovercome by washing the drawn and twisted yarns in hot water. This isundesirable in that it requires an additional processing step in themanufacture of these yarns.

it is, therefore, an object of the present invention to provide asynthetic linear polycaprolactam yarn that is free of the CililiClllikSof the prior art.

it is a further object of this invention to provide a process forproducing polycaprolactarn yarns for use in knitted articles.

An additional object of this invention is to provide a polycaprolactamyarn that when used in knitted articles produces an article of greaterwidth and improved snag resistance.

A further object of this invention is to provide a process formanufacturing polycaprolactam yarn for use in knitted articles wherebysnag resistance and width of the articles are improved.

These and other objects or" this invention will become apparent from areading of the following detailed description taken in conjunction withthe drawing.

it has been found that the objects of this invention can be accomplishedby providing a synthetic linear polycaprolactam yarn of a denier of lessthan 50. The yarn must also have a boiling water shrinkage of at least9% and a permanent birefringence when subjected to a 20% elongation.Yarn of these characteristics may be obtained by drawing undrawnpolycaprolactam yarn in a single drawing operation and during thedrawing operation, heating the yarn to an internal temperature of 140 to160 C.

The undrawn polycaprolactarn yarn may be obtained by conventionalprocesses well know to those skilled in the art. For instance,caprolactam may be polymerized by known methods and extruded intofilaments which are collected in undrawn form. The packages of undrawnyarn are then subjected to a drawing and twisting operation whichoperation may be performed on a conventional drawtwister.

To insure that the boiling water shrinkage is at least 9%, the drawn andtwisted yarn should not be washed in hot water. Such a washing operationis undesirable and it also reduces the boiling water shrinkage to lessthan 6%.

The birefringence of the yarn of this invention is permanent after a 20%elongation. This is, if at any time in the future, the yarn is subjectedto a temporary elongation of 20%, the birefringence both before andafter the elongation will be the same. This is contrary to ordinary colddrawn polycaprolactam yarn. There is no decrease in birefringence of thecold drawn polycaprolactam yarn if immediately after drawing andtwisting it is subjected to a temporary elongation. However, if the yarnis elongated at some time in the future after, for instance, about fourweeks, there will be a substantial reduction in birefrin ence of thiscold-drawn yarn. Such a decrease does not occur at this time for theyarn according to this invention.

It is believed that the desired wide and round loop formation inknitting is the result of the birefringence, remaining the same after alapse of time and an elongation. This becomes important because the yarnwill be subjected to elongation in the knitting process. Thus, it can beseen that this elongation will result in a decrease in the birefringenceof cold-drawn polycaprolactarn with an attendant undesirable stitchformation. However, if yarn according to this invention is used, therewill be no decrease in birefringence after this elongation with theresult that this yarn produces the desired stitch formation. it is,therefore, important that the birefringence remain the same even afterlong periods of storage because in normal processing several weeks andeven months elapse between the production of the yarn and its processinginto knitted article It should be understood that this above is a theoryand is not to be construed as limiting this invention.

The stitch formation obtained by using freshly drawn and twistedpolycaprolactarn yarn is slightly better than that which had been drawnand twisted several weeks before. However, this stitch formation isinferior to that of the polycaprolactam yarn of this invention.

The elongation used in measuring the decrease in birefringence ofpolycaprolactam yarn according to this invention is 20%. The yarns aresubjected to this elongation for a short period or" time, usually aboutfive seconds.

As indicated above, the polycaprolactam yarns of this invention areobtained by drawing undrawn synthetic linear polycaprolactarn yarn andheating said yarns during at least a portion of said drawing to aninternal temperature of to C. Even in drawing yarns by the cold-drawingmethod, the yarns are heated. This heat is produced by friction duringthe passage of the yarn over the cold drawn pin. However, thetemperature of the yarn of less than 50 denier is less than 100 C. andeven lower for yarn of the preferred denier of less than 32. Yarnsproduced by this method which are heated during drawing, but to lessthan the required internal temperature do not produce the desired wideand 3 round stitch upon knitting. In addition, the birefringence ofthese yarns decreases upon being subjected temporarily to a 20%elongation.

If yarn of a denier of less than 50 is heated during a portion of thedrawing to a temperature of 140 to 160 C., the polycaprolactarn yarnthus obtained will produce, upon knitting, a wide and round stitch. Inaddition, the birefringence of this yarn will not decrease whensubjected to a 20% temporary elongation. This elongation may occur atany time subsequent to the drawing and heating operation.

The internal temperature of these yarns may be raised to the required140 to 160 level by several met. ods. For instance, the draw pin or pinsmay be heated to a temperature of 100 to 110 C., preferably 105 C. Thisheat plus that generated by friction of the yarn as it passes over thedraw pin, raises the internal temperature of the yarn to 140 to 160 C.

The use of draw pins to localize the drawing of synthetic linearpolycaprolactam is well known. The yarn is passed one or more timesaround a pin which is positioned between the feed roller and draw rollerof a conventional draw-twisting machine. The wraps around the pin are tolocalize yarn drawing to an area immediately adjacent the pin.

In normal operations, no heat is supplied to the draw pins from anyexternal source other than the yarn. The only heat that is generated isthat caused by friction of the yarn as it passes over the pin. Whenprocessing yam of less than 50 denier, the yarn will, by radiation andconduction, have an internal temperature of less than 100 C.

When yarn of less than 50 denier is passed over the draw pins to whichheat from another source is applied to raise the temperature of the pinto 100 to 110 C., the yarn will have an internal temperature of 140 to160 C. This temperature can be obtained at the 531.3 or higher, ifdesired, speeds as that used in the cold-drawing operation.

The draw pins may be heated by any conventional means, such as byelectric heating elements. In addition, a heated liquid or vapor mayalso be used without departing from this invention.

It should be understood that successful operation of this invention doesnot require that the yarn be heated to the requisite internaltemperature throughout the drawing operation. It is only required thatthe yarn be heated to this temperature during at least a portion of thedrawing operation. Thus, it is possible to use heated plates or tubesbetween the draw pin and the draw roller to accomplish the requiredinternal temperature. This is because a portion of the drawing willoccur when the yarn is passed over the heated plate or through theheated tube;

The temperature of the plate or tube should be higher than that of theabove-mentioned raw pins because even though some drawing occurs afterthe yarn leaves the draw pin, it will not be as much as that whichoccurs at, the draw pin; thus, little additional heat will be developedby friction. The temperature of the plate or tube should be adjusted tothe time during which the yarn passes over the plate or through thetube. Thus adjustment is by means known to those skilled in the art. Itshould be understood that the adjustment should be sufilcient to insurethat the yarn is heated to 140 to 160 C. during this latter drawingstage.

For example, if a single filament polycaprolactam yarn of a deniersuflicient to yield after drawing a yarn of 15 denier is to be drawn ata speed of 400 meters per minute, the heated plate or tube should have ayarn passageway of 5 centimeters and a temperature of 170 C. This willinsure that the yarn is heated to an internal temperature of 140 to 160C.

It is also possible to practice this invention by heating the drawroller. This, is of course, the least preferred method of operationbecause of the small amount of drawing that occurs on the draw roller.

This invention will now be described with reference to the annexeddrawing. It should be understood that this drawing illustrates but oneapparatus capable of performing this invention.

Referring now to the drawing, reference numeral 10 denotes a syntheticlinear polycaprolactam yarn package obtained from a conventionalextrusion and winding operation. Package 10 is placed on supply point 11of a conventional draw twister indicated generally at 12. Yarn or thread13 is withdrawn from package 10 by feed roller 1 and thence around drawpin 16, which is heated to C. to C. by electrical current supplied froma source (not shown) through wires 15. Yarn 13 is substantially drawn atpin 16 by the pulling action or" draw roller 17, around which the yarnis passed. Yarn 13 is heated to an internal temperature of to C. by thecombination of the friction generated by its passing around pin 16 andthe additional heat supplied to pin 16. The difference in speed of drawroller 17 and feed roller 14 determines the draw ratio to which yarn 13is subjected.

After leaving draw roller 17, yarn 13 is twisted and collected on pirn18 by conventional twister take-up device All of the equipment discussedabove is supported in a conventional manner and the supports have notbeen shown for purposes of clarity.

The following specific examples are offered merely for the purpose ofillustration and are not to be considered as limiting the scope of thisinvention.

EXAMPLE I An unwashed and undrawn synthetic linear polycaprolactam yarnof a denier of 133 and having four filaments was withdrawn from a yarnpackage on a conventional draw twister by a feed roller. From thisroller, the yarn was passed over a draw roller operating at a suflicientspeed greater than the feed roller to draw the yarn 3.4 times its lengthbetween the two rollers thereby obtaining a yarn of a denier of 39. Thespeed of the draw roller was 375 meters per minute.

The yarn encircles, two draw pins which were positioned between the feedand draw rollers over an arc of 360. These pins had a diameter of 12 mm.and were heated to a temperature of 105 to 110 C. The yarn from the drawroller was twisted an collected by a conventional ring twister takeup.

A further sample of this yarn was processed over the same machine,except that the draw pins were not heated by an external supply of heat.The following Table I illustrates properties of these yarns. The flatwidth of the stocking is measured by laying flat a stocking that hasbeen stabilized on a form in a stream chest in a conventional manner.The flat width of the stocking is proportional to the width of thestitch.

EXAMPLE H An unwashed and undrawn, mono-filament, polycaprolactam yarnwas withdrawn from a yarn package of a conventional draw twister by afeed roller. The yarn was passed from the feed roller 360 around anunheated draw pin to and around a draw roller. The yarn was passed overa slighlty curved plate heated to C. The plate Was positioned betweenthe draw pin and draw roller and had a yarn-contacting surface of cm. inlength. The yarn was stretched between the feed roller and draw rollerto a denier of and the yarn had an internal temperature or" 143 C. as itleft the heated plate.

A similar yarn was processed in the same manner as above, except thatthe yarn was not passed over a heated plate, The following Table 11illustrates the properties of these two yarns.

Table H Heated Without plate heated plate Tensile strength/grams perdenier 7. 0 6.7 Elongation at rupture, percent 28 30 Boiling watershrinkage, percent. 13.3 13. 4 Specific birefringence 552 10- 535 10-Specific birefringence after elongat. 11 (determined 6 weeks later)552x10 518X10-4 Flat width of thigh of stocking (cotton machine, 66gauge), cm 18.0 17.3

EXAMPLE 111 An unwashed and undrawn, mono-filament, 64 denier,polycaprolactarn yarn was processed in a manner similar to that ofExample 1, except that the yarn was drawn by passing it 360 around asingle draw pin, having a diameter of 12 cm. The draw pin was heated toa temperature of 105 to 110 C. The yarn was drawn 4.3 times its lengthto a denier of 15.

A similar yarn was processed in an identical manner, except the draw pinwas not heated. The following Table III illustrates the properties ofthese two samples:

It can be seen from the foregoing examples that this invention producesa yarn that when used in knitted articles has an improved Width and onewhose specific birefringence does not decrease when the yarn issubjected to a 20% elongation. Such yarn has improved snag resistance.

It should be understood that various modifications may be made in thisinvention without departing from the spirit and scope of this inventionwhich is to be limited only by the following claims.

What is claimed is:

1. A process for drawing a continuous, unwashed, undrawn polycaprolactamfilament to produce a fine denier yarn comprising passing said undrawn,unwashed filament through a drawing zone wherein said filament is heatedin at least a portion of said drawing zone to an internal temperature offrom about C. to about C., drawing said filament a multiple of itsoriginal length in one drawing operation in said drawing zone, toprovide a drawn yarn having a denier of less than about 50, a boilingwater shrinkage of at least 9%, and a permanent birefringence whensubjected to 20% elongation, and thereafter collecting said drawn yarnwithout subjecting it to a further drawing operation.

2. The process according to claim 1 wherein the drawing of said filamentin said drawing zone is carried out by passing said filament around atleast one unheated drawing pin and said heating of said filament iscarried out by means separate from said drawing pin.

3. The process according to claim 2 wherein said heating is carried outby passing said filament over the surface of a hot plate.

4. The process according to claim 2 wherein said heating is carried outby passing said filament through a heated tube.

5. A process for drawing a continuous, undrawn, unwashed polycaprolactamfilament to produce a fine denier yarn comprising passing said undrawn,unwashed filament through a drawing Zone, wherein said filament isheated to an internal temperature of from about 140 C. to about 160 C.by passing around at least one heated drawing pin,

rawing said filament a multiple of its original length in one drawingoperation in said drawing zone to provide a drawn yarn having a denierof less than about 50, a boiling water shrinkage of at least 9%, and apermanent birefringence when subjected to 20% elongation, and thereaftercollecting said drawn yarn from said drawing zone without subjecting itto a further drawing operation.

References Cited in the file of this patent UNITED STATES PATENTS2,577,915 Piller et a1 Dec. 11, 1951 2,686,955 Luther Aug. 24, 19542,719,776 Kummel Oct. 4, 1955 2,733,122 Herele et al Jan. 31, 19562,735,840 Lynch Feb. 21, 1956 2,750,653 White June 19, 1956 2,768,057Friederich Oct. 23, 1956 2,794,700 Cheney June 4, 1957 2,869,972 Head etal. Jan. 20, 1959 FOREIGN PATENTS 811,349 Great Britain Apr. 2, 1959

1. A PROCESS FOR DRAWING A CONTINUOUS, UNWASHED, UNDRAWN POLYCAPROLACTAMFILAMENT TO PRIDUCE A FINE DENIER YARN COMPRISING PASSING SAID UNDRAWN,UNWASHED FILAMENT THROUGH A DRAWING ZONE WHEREIN SAID FILAMENT IS HEATEDIN AT LEAST A PORTION OF SAID DRAWING ZONE TO AN INTERNAL TEMPERATURE OFFROM ABOUT 140*C. TO ABOUT 160*C., DRAWING SAID FILAMENT A MULTIPLE OFITS ORIGNAL LENGTH IN ONE DRAWING OPERATION IN SAID DRAWING ZONE, TOPROVIDE A DRAWN YARN HAVING A DENIER OF LESS THAN ABOUT 50, A BOILINGWATER SHRINKAGE OF AT LEAST 9%, AND A PERMANENT BIREFRINGENCE WHENSUBJECTED TO 20% ELONGATION, AND THEREAFTER COLLECTING SAID DRAWN YARNWITHOUT SUBJECTING IT TO A FURTHER DRAWING OPERATION.